Must have been two stroke, 4 stroke motors are too large and heavy for an application like that.
According to Wikipedia
> The engine was an air-cooled, 4-stroke, 155 cc engine over the front wheel
https://en.wikipedia.org/wiki/Autoped
alt Hacker News
According to Wikipedia
> The engine was an air-cooled, 4-stroke, 155 cc engine over the front wheel
https://en.wikipedia.org/wiki/Autoped